The present invention relates to a honeycomb type (i.e., honeycomb shaped structure) gas separating membrane structure for separating or supplying a specified gas from a mixed gas. Particularly, the present invention relates to a honeycomb type gas separating membrane structure having a honeycomb unitary structure.
A method using a gas separating membrane as a method for separating or supplying a specified gas from a mixed gas has been conventionally used. Generally, a gas separating membrane selectively separates ions or atoms diffused therein. It has been known that gas permeability is inversely proportional to the thickness of the membrane. Therefore, it is preferable to reduce the thickness of the membrane as much as possible to increase the gas permeability of the gas separating membrane.
However, when the gas separating membrane is thinner than a certain degree, the mechanical strength is reduced, and the gas separating membrane cannot stand by itself. Therefore, a gas separating membrane is generally formed on an inorganic porous support made of porous glass, porous ceramics, porous aluminum oxide, or the like (e.g., Japanese Patent Publication 53-43153).
It is also preferable to enlarge the area per unit volume of the gas separating membrane to produce a compact and inexpensive gas separating membrane module. To realize this, Japanese Patent Laid-Open No. 8-40703 discloses a method for forming a gas separating membrane on a predetermined surface of a porous substrate having the shape of a monolith with through-holes, Japanese Patent Laid-Open No. 9-255306 discloses a method for forming a gas separating membrane on a metallic porous support with a metallic reinforcing plate having a plurality of gas flow holes, and U.S. Pat. No. 5,356,728 discloses a gas separating membrane which is made of a material having gas separation ability and which has a plurality of parallel through-holes running in a vertical direction so as to mutually cross each other.
Further, Japanese Patent Publication 7-67528 discloses a honeycomb porous body in a ceramic membrane structure for condensing and separating condensable gas components. It is stated that a ceramic thin membrane having numerous continuous fine pores for condensing condensable gas components are loaded on inner surfaces of partition walls. It is preferable that the fine pores have an average pore diameter of 100xc3x85 or less, and that the membrane has a thickness of 5-100 xcexcm. It is also disclosed that a porous partition wall, which becomes a support for imparting strength, preferably has an average pore diameter of 0.2-5 xcexcm and a thickness of about 0.5-3 mm.
However, in the case where a gas separation membrane is formed on a predetermined surface of a porous substrate (Japanese Patent Laid-Open No. 8-40703), it is very difficult to form a dense gas separating membrane on the porous substrate because of the difference in properties (e.g., thermal expansion coefficient) between the porous substrate and the gas separation membrane.
Another problem is that, in the case of a gas separating membrane having a layered structure (Japanese Patent Laid-Open No. 9-255306 and U.S. Pat. No. 5,356,728), though the membrane area can be enlarged, the production process becomes complex and the cost is increased.
Further, Japanese Patent Publication 7-67528 discloses that it is not considered that forming a membrane after molding a honeycomb body is necessary and a partition wall of a substrate is particularly thinned to 0.5-3 mm.
The present invention has been made in view of such conditions and aims to provide a honeycomb type gas separating membrane structure which does not require a support member for supporting the gas separating membrane, which can increase the membrane area, which has a simple production process, and which reduces costs.
According to the present invention, a honeycomb type gas separating membrane structure for separating or supplying a specified gas from a mixed gas is provided, wherein the gas separating membrane structure has a honeycomb unitary structure and is a dense body made of a material having a gas separation ability. It is preferable that a cell partition wall between a raw material gas side and a permeated gas side of the honeycomb type gas separating membrane structure has a thickness of 50-500 xcexcm. It is also preferable that a gas flow passage on the raw material gas side and a gas flow passage on the permeated gas side are disposed so that they mutually cross each other at predetermined intervals.